1. Field of the Invention
The present invention relates to a measuring method for measuring current-voltage characteristics of a photoelectric conversion device such as solar cell, photovoltaic element or photosensor under irradiation of light. In the present invention, said photoelectric conversion device includes a photoelectric conversion apparatus prepared by connecting a plurality of photoelectric conversion devices in series or parallel connection. The present invention includes a process and an apparatus for producing a photoelectric conversion device.
2. Related Background Art
The photoelectric conversion characteristics (for example, efficiency, Voc, Isc, and fill-factor) of a photoelectric conversion device such as solar cell, photovoltaic device or photosensor can be obtained by measuring current-voltage characteristics thereof under irradiation of light. The measuring method in this case includes a measuring method wherein sunlight is used as the irradiation light and a measuring method wherein artificial light source (that is, pseudo sunlight) is used as the irradiation light.
By the way, in recent years, the practical use of photoelectric conversion devices having a large light receiving face has been progressed. Along with this, necessity to measure their current-voltage characteristics under irradiation of light at an irradiance of 1000 W/m2 which is the normal irradiance of the sunlight has been increasing.
In order to precisely measure the current-voltage characteristics of a given photoelectric conversion device having a large light receiving face, it is necessary that light having an intensity of about 1000 W/m2 is uniformly irradiated over said large light receiving face of the photoelectric conversion device. When an artificial light source is used in this case, it is necessary to use, for instance, a discharge lamp with a large electric power of several tens kilowatts (kW) per an irradiation area of 1 m2 as such artificial light source. However, in order that steady light is generated by the discharge lamp with such large electric power, a large electric power is necessary to be steadily supplied, where the equipment for achieving this becomes unavoidably very large in terms of the scale. Thus, this measuring method is not realistic.
In view of this, there is known a measuring method to measure the current-voltage characteristics of a given photoelectric conversion device having a large light receiving face by using a pseudo sunlight source which generates not steady state light but pulsed light. Although no precise definition is present, as such pseudo sunlight source, there are known a long pulse solar simulator whose duration of pulsed light is more than 20 m/sec and a short pulse solar simulator whose duration of pulsed light is up to several msec. The measuring method of measuring the current-voltage characteristics of a given photoelectric conversion device having a large light receiving face by means of pulsed light in this way is more advantageous in comparison with the measuring method by means of steady state light. That is, in the latter method, there are disadvantages such that the temperature of the photoelectric conversion device is increased during the measurement and therefore, the temperature correction is necessitated. The former method is substantially free of such disadvantages.
The measuring technique by means of such long pulse solar simulator as above described is disclosed in, for instance. Japanese Patent Publication No. 4(1992)-53271 (hereinafter referred to as document 1) and Japanese Patent Publication No. 6(1994)-105280 (hereinafter referred to as document 2). Particularly, these documents 1 and 2 describe that by instantaneously flowing a large current which exceeds the rated current to a discharge lamp which is kept in a stand-by condition, it is possible to uniformly irradiate light with an intensity of about 1000 W/m2 over the entire of a large light receiving face of a photoelectric conversion device at a pulse width of more than 20 msec during the time of measuring the current-voltage characteristics of the photoelectric conversion device.
As the foregoing short pulse solar simulator, a large area pulsed solar simulator produced by Spectrolab Company and a SPI-SUN simulator produced by Spire Company are commercially available. A measuring system using said large area pulsed solar simulator as the pseudo sunlight source which is produced by Spectrolab Company and a measuring system using said SPI-SUN simulator as the pseudo sunlight source which is produced by Spire Company are also commercially available.
Now, there is known a so-called multipulse method for measuring the current-voltage characteristics of a photoelectric conversion device by using said measurement system in which the short pulse solar simulator is used as the pseudo sunlight source. According to this multipulse method, I-V data (that is, a pair of current value data and voltage value data) at n points (n is an integer of more than 2) of the photoelectric conversion device can be obtained by a manner wherein n times pulsed lights are supplied over the light receiving face of the photoelectric conversion device while applying a series of prescribed voltages to the device, where I-V data at each of prescribed n points of the device in accordance with each pulsed light while sweeping the voltage applied after the measurement of the I-V data in each case.
As the peculiar problem in the case of using the short pulse solar simulator, a problem relating to the responsibility of the photoelectric conversion device is pointed out by H. Ossenbrink et al. in the report “Errors in Current-Voltage Measurement of Photovoltaic Device Introduced by Flash Simulators” in 10th European Photovoltaic Solar Energy Conference P. 1055 (hereinafter referred to as document 3). The problem described in the document 3 is such that in the case of the photoelectric conversion device whose static capacitance is large, when the speed to sweep the voltage applied to the photoelectric conversion device is made to be faster, especially the I-V curve (the current-voltage characteristic curve) is distorted. For the reason for this, the document 3 describes that this is due to a factor that as the photoelectric conversion device has a given static capacitance, when a prescribed voltage is applied thereto, phenomena similar to the charge-and-discharge phenomena in the condenser are occurred, and in the short pulse simulator, the duration of the pulsed light is short and because of this, the time allowed to measure the current-voltage characteristics of the photoelectric conversion device inevitably becomes to be short and this makes to shorten the time allowed to sweep the voltage applied to the photoelectric conversion device.
Thus, the problem relating to the responsibility which is described in the document 3 corresponds to that relating to the responsibility of the charge and discharge of the photoelectric conversion device. Therefore, it is considered that this problem can be solved basically by measuring the current value of the photoelectric conversion device after a sufficient time is elapsed in responding to the charge-and-discharge since the time when a prescribed voltage is applied to the photoelectric conversion device.
The previously mentioned documents 1 and 2 describe the presence of a problem similar to that described in the document 3 in the measuring technique by means of the long pulse solar simulator and also describe a solution of the problem in that by prolonging the time interval for the voltage applied to the photoelectric conversion device to be changed by way of prolonging the duration of the pulsed light, it makes possible to measure the current-voltage characteristics of the photoelectric conversion device whose responsive speed to the charge-and-discharge is tardy.